From an interview with Kevin Wing, NATAS

At first going to the movie studio and practicing the song and dance wasn’t that special because by the time I was seven years old I had had bit parts in several films. As soon as I saw that set of the Munchkin Village, though, and the other 124 Munchkins who were all adults and no taller than I was, I knew I had become a member of a very special club.

The full story in Chapter 2 in the book.